Plants have historically served many medicinal purposes. The World Health Organization (WHO) estimates that 4 billion people, 80% of the world population, presently use herbal medicine for some aspect of primary health care. (WHO Fact sheet Fact sheet No 134 December 2008) However, it can be difficult to isolate the specific compound that has the medicinal effect and to reproduce it on a commercial scale. Additionally, while active compounds may be isolated from a plant, the other parts of a plant such as the minerals, vitamins, volatile oils, glycosides, alkaloids, bioflavanoids, and other substances may also be involved in the functioning of the active ingredient or the medicinal effect for which the plant is known, making the use, purification and commercialization of plant based pharmaceutical agents a challenge.
Phorbol is a natural, plant-derived organic compound of the tigliane family of diterpenes. It was first isolated in 1934 as a hydrolysis product of croton oil derived from the seeds of Croton tiglium, a leafy shrub of the Euphorbiaceae family that is native to Southeastern Asia. Various esters of phorbol have important biological properties including the reported ability to mimic diacylglycerols and activate protein kinase C (PKC); and to modulate downstream cell signaling pathways including the mitogen-activated protein kinase (MAPK) pathways. Phorbol esters are additionally thought to bind to chimaerins, the Ras activator RasGRP, and the vesicle-priming protein Munc-13 (Brose N, Rosenmund C., J Cell Sci; 115:4399-411 (2002)). Some phorbol esters also induce nuclear factor-kappa B (NF-κB). The most notable physiological property of phorbol esters is their reported capacity to act as tumor promoters. (Blumberg, 1988; Goel, G et al., Int, Journal of Toxicology 26, 279-288 (2007)).
12-O-tetradecanoylphorbol-13-acetate (TPA), also called phorbol-12-myristate-13-acetate (PMA), is a phorbol ester used in models of carcinogenesis as an inducer for differentiation and/or apoptosis in multiple cell lines and primary cells. TPA has also been reported to cause an increase in circulating white blood cells and neutrophils in patients whose bone marrow function has been depressed by chemotherapy (Han Z. T. et al. Proc. Natl. Acad. Sci. 95, 5363-5365 (1998)). However, due to a variety of factors, including caustic reactions when contacted with the skin and concerns for its potential toxicity, TPA has not been shown to be an effective adjuvant to chemotherapy. Indeed, as phorbol esters play a key role in activation of protein kinase C, which triggers various cellular responses resulting in inflammatory responses and tumor development (Goel et al., Int, Journal of Toxicology 26, 279-288 (2007)), phorbol esters would generally be excluded from possible treatment candidates for neoplasms including cancer.
Cancer is one of the leading causes of death worldwide accounting for 7.6 million deaths (around 13% of all deaths) in 2008 (GLOBOCAN 2008 (IARC) Section of Cancer Information (Aug. 12, 2011)). Globally, 12,662,600 new cases were diagnosed in 2008. (2008 (GLOBOCAN 2008 (IARC) Section of Cancer Information (Aug. 12, 2011)). In the U.S. alone, 1,596,670 new cases of cancer were diagnosed in 2011 (Cancer Facts & Figures—2011, American Cancer Society (ACS), Atlanta, Ga., 2011).
Cancer treatments generally involve a combination of surgery, chemotherapy, hormonal therapy and/or radiation treatment to eradicate neoplastic cells in a patient. However, current therapeutics for neoplasms have a number of drawbacks including insufficient potency and intolerable side effects. Surgery, for example, may be contraindicated due to the health of a patient. Additionally, it may be difficult to obtain clear margins around a tumor, resulting in some neoplastic tissue being left behind and an increased chance of recurrence of the disease.
Generally, chemotherapeutics act by killing cells that divide rapidly, one of the main properties of most cancer cells. However, they also harm normal cells that divide rapidly such as cells in bone marrow, the digestive tract and hair follicles. They frequently have significant side effects including severe nausea, bone marrow depression, and immunosuppression.
Ionizing radiation works by damaging the DNA of exposed tissue. However, while targeted, it can still damage normal cells as well as neoplasms and can have side effects such as anemia, nausea and vomiting, poor appetite, weight loss, constipation, diarrhea, hair loss, and infertility.
For many patients, the toxic side effects of current therapies diminish their quality of life to such an extent they simply stop taking their medications. For others, therapeutic schedules are so complicated and inconvenient that compliance is limited. Other patients experience excellent results initially, but suffer relapses despite full compliance with therapeutic regimens. There is clearly a need for new and more effective treatments for neoplasms and to manage the side effects of current treatments for neoplasms including cancer.